1. Field of the Invention
The present invention relates to a wireless communication system, and more particularly, to a method and apparatus for detecting a transmission symbol using a lattice-reduction matrix in a Multiple Input Multiple Output (MIMO) system.
2. Description of the Related Art
In a wireless transmission/reception system, a symbol transmitted from a transmitter may be distorted by influences of multipath, signal attenuation, noise, etc., and a receiver will receive a distorted symbol if such signal distortion occurs. In this case, the receiver should restore the original transmission symbol transmitted from the transmitter, using the received signal and channel characteristic information.
Recently, research has been conducted on a Multiple Input Multiple Output (MIMO) system which increases a data transfer rate by utilizing a plurality of antennas. The MIMO system can maintain a high data transfer rate because it transmits data simultaneously using a plurality of antennas, but requires a large amount of calculations to exactly detect transmission symbols, which complicates the structure of a receiver and makes the implementation of the receiver difficult.
Representative linear detection methods that are used in the MIMO system are based on zero-forcing (ZF), minimum mean square error (MMSE), or successive interference cancellation (SIC). Also, utilizing a BLAST-ordered decision feedback (BODF) detector is the simplest detection method. However, in the case of an ill-conditioned channel matrix, the linear detection methods have not shown excellent performance compared to utilizing a maximum likelihood (ML) detector. Accordingly, in order to solve the problem, a variety of detectors have been developed.
A lattice-aided detector has performance higher than those of SIC detectors or linear detectors with low complexity, and calculates a lattice-reduction matrix in order to transform a system matrix to an equivalent one with a better conditioned channel matrix. The lattice-reduction matrix can be calculated by an LLL (Lenstra, Lenstra, Lovaz) algorithm, etc. Meanwhile, a double-sorted low complexity lattice-reduced decision-feedback (DOLLAR) detector can be utilized as a lattice-aided detector. However, since the conventional detection method using the lattice-reduction matrix does not provide a soft output, it is difficult to obtain coding gain by soft decision channel decoding.